[NOTE: To make this install/swap infinitely simpler, Wiring Specialties makes an OEM-appearing harness that will save you a TON of time and hassle. Their RB-into-240sx harness is top-notch!]

Electrical Harness at Engine: 1) Trace engine coolant temp sensor wire, label it, and leave in the engine bay. 2) Take note of the KA injector wires (B/R), cut this wire at KA injectors.These wires will be used for the RB.The rest of the KA wiring harness I removed and used the shielding on extended wires. I also cut the other wires to extend the RB harness wires. 3) Label and disconnect KA lower harness in engine bay. 4) Label and disconnect fuel feed and return lines at fuel filter, heater hoses at firewall, and throttle connections.

-Disconnect exhaust at catalytic converter. -Disconnect AC lines at firewall and condenser.(After it has been evacuated of Freon) -Disconnect power steering reservoir and lines. -Label and disconnect power brake booster hose from engine. -Remove shifter from transmission. -Attach hoist to KA. -Remove engine mount nuts from both lower side of the mounts. -Remove transmission mounts and support with a rolling jack. -Remove drive shaft and seal the rear of the transmission to prevent oil spill. -Pull out KA and transmission as one unit. -Place front of car on jack stands. -Remove power steering lines (if not using PS).

RB25DET and Transmission Installation: -Assemble RB and transmission.Flywheel 105-112 ft/lbs.Pressure plate 25-33 ft/lbs. -Install engine mount adapter plates on x-member.Leave loose. -Indent firewall 1-1.5” at starter area.That is actually the wrong spot.Indent the bump that is at 7 o’clock from where I dented it. -Install engine and transmission as one unit with a hoist.Once motor is close to mounts, place a jack under the transmission and raise until transmission is level with the engine.Lower the engine to the mounts and tighten the rubber isolator nuts (x2).Keep bolts on engine mounts to x-member loose. -Install new transmission mounts (using bolts from old mounts) to the transmission housing. -Raise transmission into position (shifter cover level with the tunnel) and bolt transmission mount to chassis.Leave loose. -Place jack under oil pan and take pressure off engine mounts. -Tighten the mount bolts to cross-member (x4) 51-58 ft lbs. -Use a pry bar and push the transmission to the passenger side and tighten the rest of the transmission bolts 16-21 ft lbs. -Inspect clearance between steering shaft and O2 housing (3/32-1/4”).If not enough clearance, the transmission bolt holes may need to be slotted. -Once satisfied with the engine and transmission placement, drill a hole on the x-member and bolt the engine mount adapter wings to the cross-member.

**According to my understanding, based upon “Your 8 step program to your RB25 starting”; NICO Forums, by opensource. Before disconnecting and cutting wires, it is best to understand what you will need to connect to what wire. Do this by looking at both (KA and RB) ECU diagrams and actual ECU’s.Label all the wires according to “Steps” and double check everything. Use wires and shield tubing from KA wiring harness to extend MAF sensor.·**

1. Attach twin power connector to positive terminal.It’s the red plastic connector which will power the engine room and dash harness. Also attach the RB lower engine harness to the positive terminal (from the alternator, starter, etc.)·2.The RB harness’ white main plug (B-82) has been cut off close to the bundle.Cut all of KA wiring harness that will be used at the ECU plug.All wiring connections will be done at the RB wiring bundle close to the ECU inside the car.I will refer to this as the “white plug”. The big bundle to the right is the RB “white plug”.·3.From the brown KA plug under the dash above the ECU, connect the Orange wire (#34 Start Switch @ ECU) to the RB white plug Grey/Red wire (AF09 Start Switch).·4.From the KA ECU plug, connect Red wire (101 ECCS Relay) to RB white plug Red wire (AF04 Ign Relay).·5.From KA ECU plug, connect Black/Red wire (#36 Ign Switch Fuse) to RB white plug Black/Red wire (AF36 Ign Relay).Get this B/R wire from the KA wiring harness.Refer to step 8 of “KA24de and transmission removal”.This is the wire that was cut at the KA injectors.·6.From RB connector A-? , need to connect RB Grey wire (AF81 Injectors) to the B/R wire connection in step 4b (AF36 Ign relay)..7.From KA ECU plug, connect Black/Pink wire (#104 Fuel Pump Relay) to RB white plug Black/Pink wire (AF73 Fuel Pump Relay).·8.Break for a beer.·9.Connect main battery ground wire from the RB engine block to the chassis.·10.RB lower engine harness olive plug, connect the Black/White wire (Starter Ground?) in this plug to the Black/Yellow wire from the KA. Grey plug at the bottom of the fuse box near the battery location.This is the only thing to connect in the engine bay in this 8 step wiring..Continuation of Wiring:.11.RB white plug Red/White wire (AF10 Check Engine Light) connect with KA ECU plug Red Wire (#24 Malfunction Indicator Lamp)..12.RB white plug Yellow/Lavender wire (MF01 Tachometer Out [#7 on ECU]) connect to KA ECU plug Yellow/Red (#2 Tachometer) and RSM Yellow wire.There are 2 Y/L wire at RB white plug so make sure you attach the right one..13.RB white plug Yellow/Green wire (MJ04 Hicas Diagnostic Wire/ Speed Limiter) connect to KA ECU plug Yellow/Green (#32 Electronic Speedometer) and RSM Pink wire (connect close to ECU) and Purple wire (connect distal to ECU).Note:Speedometer on RSM is km/h and mine is completely inaccurate.I am using my KA electronic HUD speedo in km/h and it is 10 mp/h off..14.RB ECU #59 Black/White connect to RSM Red wire (Ign Power)..15.RB ECU #50 Black connect to RSM Black wire (ground)..Note:steps 12 and 13 you can actually connect at the RB ignition relay.That is one of the 2 relays located close to the ECU..16.Check the wire color for the engine temperature gauge at the back of the KA gauge cluster and connect it with the RB temp wire.Sorry, did not make note of the color..17.Connecting speedometer wires at engine bay: RB lower engine harness Grey plug, take Grey/Red and Yellow/Purple wires.Find KA Grey plug (mine was clipped to the side of the fuse box) which contains Yellow/Lavender and Yellow/Black wires.Connect Y/B to G/R and Y/L to Y/Pu.See picture.The KA wires came from that plug next to my little finger.. Place OBX shifter on transmission..Note:the original KA shifter bushing at the end of the shifter will still work, although much smaller compared to the RB.Just some extra slop on the shifter. . -Connect McKinney drive shaft. -Connect down pipe, test pipe and exhaust. -Connect vacuum lines. -Connect throttle cable. -Connect heater hoses. -Connect fuel feed and return lines. -Attach MAF with intake. -Place oil filter. -Fill fluids.Engine oil, coolant, transmission oil, brake fluid in the clutch reservoir (and bleed the line). -Connect battery terminals. -Crank engine a few times to get oil pressure and lubricate engine. -Replace fuel pump fuse. **Cross fingers and start engine.

Disclaimer:To the best of my knowledge this information which I gathered is correct.This is the step-by-step instruction that I used when I did my swap.This information is my compiled research from the internet forums and manufacturers instructions.It is best that you do your own research and only use this as a reference.Therefore, I am not accountable for any screw ups.My mechanical experience is very limited and you should double check everything with other sources that is more qualified than me.